Each year in the United States of America, influenza viruses are responsible for seasonal epidemics resulting in over 200,000 hospitalizations and 30,000–50,000 deaths. Accurate and early diagnosis of influenza viral infections are critical for rapid initiation of antiviral therapy to reduce influenza related morbidity and mortality both during seasonal epidemics and pandemics. Morbidity and mortality may be extremely severe, and young adults and children may be affected in large numbers. In the 21st century, the global spread of pandemic in?uenza is likely to be very rapid.

The host-pathogen interaction is defined as how microbes or viruses sustain themselves within host organisms on a molecular, cellular, organismal or population level. This term is most commonly used to refer to disease-causing microorganisms although they may not cause illness in all hosts. Microbes were thought to be primary aggressors that governed the host-pathogen interaction, resulting in disease. Host damage was the most relevant outcome of the host-pathogen interaction.

Early diagnosis of influenza viral infections are critical for rapid initiation of antiviral therapy to reduce influenza related morbidity and mortality both during seasonal epidemics and pandemics. Several different approaches are currently available for diagnosis of influenza infections in humans. These include viral isolation in cell culture, immunofluorescence assays, nucleic acid amplification tests, immune chromatography-based rapid diagnostic tests, etc. Newer diagnostic approaches are being developed to overcome the limitations associated with some of the conventional detection methods. The rapid flu swab test is a relatively fast and accurate method for diagnosing influenza.

Antiviral medications are a second line of protection framework against flu contamination. The antiviral medications have been affirmed for treatment of intense uncomplicated flu and for some preventive employments. Tamiflu (oseltamivir phosphate), Relenza (zanamivir) and Rapivab (peramivir) are the three FDA-affirmed flu antiviral medications suggested by CDC for use against as of late coursing flu infections. There is a great need for antiviral drugs with increased potency and decreased toxicity. The Center for Disease Control and Prevention has estimated that routine immunization of newborns prevents about 42,000 deaths and 20 million cases of disease each year, saving about $13.6 billion.

The neuraminidase inhibitors zanamivir and oseltamivir interfere with the release of progeny influenza virus from infected host cells, a process that prevents infection of new host cells and thereby halts the spread of infection in the respiratory tract. The neuraminidase inhibitors are effective against all neuraminidase subtypes and, therefore, against all strains of influenza, a key point in epidemic and pandemic preparedness and an important advantage over the adamantanes, which are effective only against sensitive strains of influenza A. These new drugs, if used properly, have great potential for diminishing the effects of influenza infection. The global neuraminidase inhibitor susceptibility network (NISN), which coordinates the analysis of clinical isolates collected through the World Health Organization's surveillance network, found no influenza isolates with spontaneous resistance to neuraminidase inhibitors.

Influenza viruses are constantly evolving, in fact all influenza viruses undergo genetic changes over time. Hemagglutinin (HA) or Haemagglutinin (BE) is an antigenic glycoprotein found on the surface of the influenza viruses. It is responsible for binding the virus to the cell that is being infected. Understanding the relationship between antigenic structure and immune specificity, the receptor binding specificity in virus transmission, how the cleavage site controls pathogenicity, and how the fusion peptide causes membrane fusion for the entry of influenza virus into the host cell should provide information to find more effective ways to prevent and control influenza.

Influenza epidemics, also known as seasonal flu, occur annually and are
the most common emerging infection among humans. These epidemics have
major medical impacts, but they are generally not fatal except in
certain groups such as the elderly. Emerging and re-emerging epidemic
diseases pose an ongoing threat to global health security. The WHO’s
twelth general programme of work sets the reduction of “mortality,
morbidity and societal disruption resulting from epidemics, through
prevention, preparedness, response and recovery activities” as one of
its five strategic imperatives.

Influenza pandemics occur when a novel influenza virus emerges against which the vast majority of the world’s population has no immunity. Pandemics, on the other hand, happen once every few decades on average. They occur when a new subtype of influenza A arises that has either never circulated in the human population or has not circulated for a very long time (so that most people do not have immunity against the virus). The new subtype often causes serious illness and death, even among healthy individuals, and can spread easily through the human population. Yet despite the legacy of the 1918 “Spanish flu,” estimated to have killed at least 20 million people and the additional deaths, social disruption, and economic losses that resulted from pandemics in 1957 and 1968, the general public appears relatively unconcerned about the next “killer flu.” Depending on its severity, an influenza pandemic could result in 200,000 to 2 million deaths in the United States alone.

Epidemiology deals with the incidence, distribution, and possible control of diseases and other factors relating to health. Epidemiology is the study and analysis of the patterns, causes, and effects of health and disease conditions in defined populations. It is the cornerstone of public health, and shapes policy decisions and evidence-based practice by identifying risk factors for disease and targets for preventive healthcare. Epidemiologists are concerned with study design, collection and statistical analysis of data, amend interpretation and dissemination of results. Evolutionary epidemiology spans a broader spectrum of host-parasite relationships. In tropical and sub-tropical regions, the disease usually occurs year-round, although seasonal peaks of increased activity may be observed.

Emerging infectious diseases have been increasing in incidence and are a key threat to wildlife and human health. Influenza naturally infects wild birds all around the world, although they usually do not become ill. The virus is very contagious, however, and it can become a problem when the virus is transmitted to domesticated birds, such as chickens, ducks, or turkeys, because domesticated poultry can succumb to illness and death from influenza. Since 1997, H5N1 infections in birds have spread, initially throughout Asia. Then as birds traveled along their migratory routes, H5N1 dispersed to Russia and Europe, and later to countries in the Middle East and on the African continent. Wild and domestic birds are recognized as the reservoirs of most influenza A viruses. Although the extent to which birds are involved in the emergence and global spread of novel, pandemic human strains remains debated, even the most recent pandemic strain, H1N1, contains several segments that most likely originated in birds. Thus, the dynamics of influenza infections among birds and mammals (including humans) are intimately linked.

The immune response to influenza A virus infection involves both B and T lymphocytes. The innate immune system triggers the body's "emergency response" to invaders such as infections. This rapid attack gives the body's adaptive immune system time to generate antibodies that specifically target the virus or bacterium. Flu vaccines train this adaptive immune system to attack specific viral strains.

There are four types of influenza viruses: A, B, C and D. Human influenza A and B viruses cause seasonal epidemics of disease almost every winter in the United States. The emergence of a new and very different influenza A virus to infect people can cause an influenza pandemic. Influenza type C infections generally cause a mild respiratory illness and are not thought to cause epidemics. Influenza D viruses primarily affect cattle and are not known to infect or cause illness in people. There are many other non-flu viruses that can result in influenza-like illness (ILI) that spread during flu season.

Mathematical models of viral infection have been successfully applied to a number of problems on the periphery of the annual public health problem that is influenza. In the laboratory, mathematical models have aided the development of efficient vaccine production techniques and improved the quantitative characterization of antiviral drug action. Mathematical models have also improved our understanding of the course of the disease within human and animal hosts. Because these models serve as a bridge between the microscopic scale (where virus interacts with cell) and the macroscopic scale (where the infection is manifested as a disease) they will inevitably be applied in the future to pressing public health questions such as the estimation of virulence and fitness for emerging strains, the spread of drug resistance and, more generally, the connections between viral genotypic information and clinical data.

Influenza virus infections cause seasonal epidemics, affecting millions of people worldwide. The World Health Organization (WHO) estimates ~300,000-500,000 deaths per year worldwide due to seasonal influenza and more than $26.8-87.1 billion/year in healthcare costs in the United States alone. Influenza, a segmented RNA virus achieves part of its ongoing virulence as a result of its strikingly high mutation rate, typically reported for Influenza A viruses of ~2 to 2.5 × 10-3mutations/site/year. Thus, is the intense effort and energy devoted to achieving effective long-term human and veterinarian vaccines. Currently, licensed influenza vaccines are either trivalent (three influenza strains) or quadrivalent (four influenza strains), as either an injectable inactivated whole virus (IIV) or a nasal spray live attenuated vaccine (LAIV). Although efficacious, standard traditional Influenza vaccine production is laborious, only moderately high-throughput and requires physical plants housing and/or incubating millions of specific-pathogen-free eggs. Research targeting alternate strategies has been prodigious, both at the preclinical and even Phase I clinical level, and has investigated approaches such as split virion, subunit, DNA, and viral vectored vaccines. Among the recently-explored, more novel and potentially-promising strategies has been recombinant particulate vaccines generally comprising virus-like particles or nanoparticles.

Influenza viruses are constantly evolving, in fact all influenza viruses undergo genetic changes over time. The information CDC collects from studying genetic changes (also known as “substitutions,” “variants” or “mutations”) in influenza viruses plays an important public health role by helping to determine whether existing vaccines and medical countermeasures (e.g., antiviral drugs) will work against new influenza viruses, as well as helping to determine the potential for influenza viruses in animals to infect humans.

Respiratory diseases today are a major global health problem. In the world, the influenza and acute respiratory viral infections(ARVI)cause the main economic damage in the structure of infectious respiratory diseases.Respiratory viruses are the cause of a large burden of disease in humans and although effective vaccines exist to protect against seasonal influenza,no vaccines are currently available for other important human respiratory viral diseases such as avian influenza, pandemic influenza and respiratory syncytial virus (RSV) infection.Respiratory infections represent a leading disease burden in developing countries and emerging markets. The respiratory syncytial virus (RSV) diagnostics market size was valued at USD 567.1 million in 2014 and is expected to grow at a CAGR of 9.6% over the next seven years.

North America dominated the Respiratory Syncytial Virus diagnostics market in 2014 with over 40.0% share. Increasing incidences of respiratory infections and supportive initiatives by government and healthcare agencies such as Pan American Health Organization (PAHO) to mandate screening of newborns for crucial infections and metabolic disorders are anticipated to propel the RSV diagnostics market within the region.According to the CDC, rising volume of hospitalization due to RSV infection that may lead to mortality is being observed within American regions, thereby propelling the need for early diagnosis.Asia Pacific is anticipated to witness the fastest growth for the Respiratory Syncytial Virus diagnostic industry over the forecast period. Owing to the moderate standards of living, prevalence of infectious diseases is comparatively high in the countries of this continent, which demands for better diagnostic and treatment options.The key players of the Respiratory Syncytial Virus diagnostics market include Ortho Clinical Diagnostics, Roche Diagnostics, Thermo Fisher Scientific Inc., Abbott Laboratories, Becton Dickinson and Company, EMD Millipore, Coris BioConcept, Quest Diagnostics, Alere Inc., and others.

On the basis of geography, global parainfluenza virus diagnostic testing market is segmented into five key regions viz. North America, Latin America, Europe, Asia Pacific, and Middle East & Africa. North America is projected to hold largest shares in the global market primarily due to growing incidence of parainfluenza virus and innovations in diagnostic techniques. Asia pacific human parainfluenza virus diagnostics testing market is anticipated to witness prominent growth during the forecast period owing to increased healthcare expenditure and repeated outbreaks of infectious diseases in developing countries such as India and China.

The vast majority of URIs have a viral etiology. Rhinoviruses account for 25 to 30 percent of URIs; respiratory syncytial viruses (RSVs), parainfluenza and influenza viruses, human metapneumovirus, and adenoviruses for 25 to 35 percent; corona viruses for 10 percent. Currently, the most common causes of viral LRIs are RSVs. Both bacteria and viruses can cause pneumonia.The burden of LRIs caused by Hib or S. pneumoniae is difficult to determine because current techniques to establish bacterial etiology lack sensitivity and specificity.Measles virus, RSVs, parainfluenza viruses, influenza type A virus, and adenoviruses are the most important causes of viral pneumonia.

Interventions to control ARIs can be divided into four basic categories: immunization against specific pathogens, early diagnosis and treatment of disease, improvements in nutrition, and safer environments.The first two fall within the purview of the health system, whereas the last two fall under public health and require multisectoral involvement.The efficacy of Hib vaccine in preventing invasive disease (mainly meningitis, but also pneumonia), has been well documented in several studies in industrialized countries. The initial promise and consequent general perception was that Hib vaccine was to protect against meningitis, but in developing countries the vaccine is likely to have a greater effect on preventing LRIs.Hib vaccine was introduced into the routine infant immunization schedule in North America and Western Europe in the early 1990s. wider use of available vaccines will reduce ARI mortality among young children by half to two-thirds. The systematic application of simplified case management alone, the cost of which is low enough to be affordable by almost any developing country, will reduce ARI mortality by at least one-third. The urgent need is to translate this information into actual implementation.